1. Field of the Invention
The present invention relates to a circuit for controlling the power supplied to an electrode of the shielded type as used in an electric arc welder device. These shielded electrodes are well known in the art as being solid flux covered metal electrodes used in shielded metal arc welding process (SMAW). Such a power control protects welders against electric shocks in limiting the open circuit voltage between the electrode and the workpiece to be welded to a safe level.
In welding operations, welders who have to work with electric arc electrodes which require a rather high starting voltage are quite commonly subjected to electric shocks, particularly when the welding operation is effected in a damp environment, such as on hydraulic turbines, in tanks or basins, in water cooling systems, where it is extremely difficult to obtain adequate electric insulation between the welder and the grounded workpiece or electrode holder. It has been observed that electric shocks frequently occur and are strong enough to inflict in the welder a nervous repulsive feeling against electric shocks, although these shocks usually do not result in severe injuries. A feature of the present invention generally resides in eliminating electric shock hazards by controlling the open circuit voltage of the electrode-workpiece assembly, such a voltage corresponding to that necessary for starting the electric arc.
2. Description of Prior Art
It is known that there exists a high probability of electric shocks when the arc starting voltage, usually of about 80 volts, is developing in the open circuit formed between the electrode and the workpiece. When started, the electric arc is maintained burning under a much lower voltage ranging from about 15 to 30 volts. To reduce electric shock hazards associated with high open circuit voltage, there was proposed various types of manually or automatically operated circuits incorporating mechanical contactors, the main function of which was to disconnect the electrode from the power supply when the electric arc was off. However, those mechanical contactors suffer from a major drawback, in that they have a low time response. None of the suggested circuits have ever offered a reliable and efficient answer to the security problems associated with the use of electric arc electrodes. Thus, the prior art circuits have never achieved acceptance among welders.